Fish Fossil Shows Evolutionary Beginning Of The Jaw

"Left: This is an illustration of Metaspriggina swimming. This is a fossil of Metaspriggina from Marble Canyon -- head to the left with two eyes, and branchial arches at the top"

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Researchers have identified a "key piece of the puzzle" in the evolution of vertebrates.

An ancient fish, dubbed Metaspriggina, shows arches near the front of its body that may have been the beginning stages of jaws, a University of Cambridge news release. This is the first time this has been seen in such a well-preserved manner.

The fossil was recovered from the Burgess Shale site in Canada. The fossils at the site tie into the Cambrian explosion, which was a period of rapid evolution that started about 540 million years ago.

Before this finding was made only two Metaspriggina fossils were known to scientists, and these were not as well-preserved.

"The detail in this Metaspriggina fossil is stunning," said lead author Professor Simon Conway Morris of Cambridge's Department of Earth Sciences, said in the news release. "Even the eyes are beautifully preserved and clearly evident."

Pre-vertebrate fossils are difficult to find because they are composed of mostly soft-tissue, which is rarely preserved. This new well-preserved specimen can help researchers identify details such as how the fish swam.

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The branchial arches were once believed to be a series of single arches, but this new specimen shows that they actually existed in pairs.

"Once the jaws have developed, the whole world opens," Morris said in the news release. "Having a hypothetical model swim into the fossil record like this is incredibly gratifying."

"Obviously jawed fish came later, but this is like a starting post - everything is there and ready to go," the paper's co-author Doctor Jean-Bernard Caron, Curator of Invertebrate Palaeontology at the Royal Ontario Museum and associate professor in the Departments of Earth Sciences and Ecology & Evolutionary Biology at the University of Toronto, said in the news release. "Not only is this a major new discovery, one that will play a key role in understanding our own origins, but Marble Canyon, the new Burgess Shale locality itself has fantastic potential for revealing key insights into the early evolution of many other animal groups during this crucial time in the history of life."